232 OLAF GALL0E 



The species here enumerated, which occur on rock and on 

 earth, consequently represent what may be called the nival lichen- 

 llora of Iceland; they are the most hardy species, and ascend far 

 above the coppices, heaths and grass-carpets, right up to the snow- 

 line. With regard to the majority of them it may be asserted 

 as already mentioned that they also descend far into the low 

 land; only Solorina crocea and Usnea melaxantha can with certainty 

 be regarded as exclusively mountain-height plants. 



But in addition to the species mentioned here, various others 

 will no doubt be found in the future, when more mountain sum- 

 mits and the interior plateau of Iceland have been better investi- 

 gated. 



In the above, when discussing the earth-lichens, those species 

 have been mentioned, which are found in the common earth-plant- 

 associations, as far as these, taken as a whole, bear lichens. The 

 lists of species given there, are consequently also illustrative of the 

 vertical distribution of the lichens, inasmuch as the heath with its 

 lichens ascends to about 300 metres up the mountains, the birch cop- 

 pices to about 550 (more frequently less), the willow-coppices (which 

 do not appear to be very widely distributed and are almost unknown 

 as regards their lichens) to about 800 metres, the grass- vegetation, 

 with the upper limit of which I am not acquainted, and the desert- 

 vegetation up to 1000 1400 metres; then comes the ice-region. 



If we now go through the lists, which are given above for each 

 individual association grass, heath, moss, coppice, etc. we 

 shall find that they do not include all the earth-lichens of Iceland, 

 inasmuch as they do not contain all the numerous species, which 

 have in part been found by other collectors without their having 

 stated more closely in which association they were collected. Conse- 

 quently, here is a large field left for future investigations, i. e. an 

 elucidation with regard to the particular association in which each 

 single species lives and together with this association - - at what 

 sea-level. 



With regard to the mass-occurrence of the earth-lichens at 

 various altitudes, very much is likewise wanting to our possession 

 of reliable data as regards the heights, which are most favourable 

 to them. This much can only be said as a general fact, that (1) 

 close to the sea no lichens live on the earth, if the ground-water 

 reaches to the surface of the earth; and (2) from these low altitudes, 

 and upwards, the mass-occurrence of the lichens appears to be 



